Roasting furnace



May 19, 1925.

I 1,538,794 L. sscnwmo noxsrrma FURNACE Filed Sept. 19. 1923 May 19, 1925.

L. GESCHWIND ROASTING names Filed Supt. 19. 1923 2 Shuts-She 2 mental J. 6 esclullrb'zvd/ latented May 19, 1925..

LUornN ensonwrnn, or PARIS, FRANCE.

ROASTING FURNACE.

Application filed September is, 1923. sci-m1 No. 663,714..

To all whom it may concern:

Be it known that I, LUcinN Gnsonwrnn,

ing at 117 Ed. Haussmann, Paris, France, have invented certain new and useful Improvementsin Roasting Furnaces, of which the following is a specification.

My invention relates to roasting furnaces of the Spirlet type.

The Spirlet furnaces comprise a plurality of circular hearths of refractory material which are superposed and are alternately fixed and movable. Each hearth consists of a thick plate of refractory substance which is slightly convex at the top, said plate being mounted in a circular metallic frame. The frames of the fixed hearths are secured to a stationary structure Whilst the" frames of the rotating hearths comprise an outer circular rail resting upon rollers whose axles are secured to the said stationary structure; the movable hearths are rotated by suitable means. The teeth of the raking portion consists of blocks of refractory material having the shape of triangular prisms with vertical edges whose rectangular base is embedded in the lower face of each fixed hearth, said blocks being disposed according to a spiral, or at least in such manner that the operation of each block shall not be hindered by the succeeding block and that the proper cleaning will be ensured.

The said furnaces are used at the present time solely for the roasting of zinc blende. By reason of the close spacing of the hearths and the reduced radiation, the com bustion is very active and temperatures of 850 to 900 degrees C. are readily attained.

Since it is important for the roasting proccss as well as for the preservation of the refractory material thatsuch temperatures should not be exceeded, only days run. furnace having 4.70 metres diameter with four hearths whereof two are movable, may provide for a daily chargeof' 4; to 5 tons of leadbearing zinc blende con taining 14 per cent of lead and 28 per cent sulphur. The oxidizing air should be sup plied in the heated state,.but this requires the use of coal in the proportion of some 6 per centof the raw ore.-

In a furnace of this class it is only feasible to roast from 2 to 2.5 tons of pyrites per day, by reason of the heat produced by a relatively small quantity; of ore can be treated 1n a the combustion of the ore which for a given weight of ore is much greater than 1n the a citizen of the French Republic, and residcase of zinc blende, since the pyrites contain about 50 per cent of sulphur and its combustion is more exothermic.

Metallic teeth, even when cooled by a circulation of air, are unable to withstand the high temperatures prevailing in the furnace, so that it becomes necessary to use clay for their construction; but the clay is found to combine with the elements of the zinc blende, chiefly the lead, thereby forming crusts containing silicate and lead.

For this reason the said teeth must be cleaned several times a day with a metallic tool, thus requiring hand labour and causing breakage; such teeth cannot in fact last for more than from 3 to 6 months in the regions of the greatest heat, and this requires a frequent stoppage of the furnace and reconstruction of the hearths.

But with the clay in current use it is not feasible to make teeth which have a flat shape, as .these would be very easily broken, and hence it was found necessary to give to such teeth the shape of a triangular prismatic mass whose large part is situated at the rear; in this case the hearth is covered during the raking operation by the whole sur face of the said rear portion, leaving between each row of ore an empty annular space having in fact the width of this rear art.

Further, depending as before upon the fragile nature of the clay, it was not feasible to employ a great number of teeth and to give them when proceeding from the centre a suitable section corresponding to the reduced amount of the rows of ore relative to the diameter, so that when proceeding towards the exterior, the annular prisms of ore become continually of smaller size, and hence the surface of the hearth is utilized for the roasting in a very defective manner and the amount of ore circulating inthe furnace is very small. But sincethere is a direct relation between the sojourn of the material in the furnace, name ly, the duration of the roasting, and the weight of the material within the furnace, the ore will remain but a short time in the Spirlet furnace, and in fact this may be estimated at only six hours.

On the other hand, the raking plane of the tooth is vertical, so that during the travel of the mass of ore when roasting, the

and by providing fora thorough stirring of the ore. The firstmentioned drawbacks, namely, relating {t the temperature, the formation of crusts andthe like, are eliminated in our present invention by the use of special metal-lie rakes which are of hollow construction and are water-cooled. Each hearth consists of two like halves made of refractory materia'lbetween which is fitted a diametrical rake of thesaid type, made of cast iron or steel, it being supported in the same manner as the hearth by the circular metallic frame of the latter; for the sta- -.tionary hearths, the rake is hollow for the .entire length, and the water .enters at one .end and is discharged at the other; for the movable zhearths, the water inlet and outlet are both disposed at thecentral partof .the rake, employing two concentric tubes situated upon the axis of the furnace.

(ith 'the said arrangement. combined with ,theabovesmentioned special teeth, I am enabled with the use of a Spirlet furnace .of ,the size above stated to attain and even to exceed a daily output of 801' 9 tons of Zincblende having 28 per cent sulphur this being double .the usual output, while at the same time dispensing with the auxiliary heating required with the Spirlet furnace.

lVith the same furnace 1 was enabled :to at- ;tain .a daily output of 6 to 7 tons of pyrites.

The following description and appended drawings relate to a constructional form vof .the improved furnace according to the in vention.

F 1 represents in section and in eleva- .tion, with parts broken away, the general arrangement of a Spirlet furnace comprising the .devices according to the invention.

Figs. 2 and 3 represent onasmaller scale diagrammatic plan views .of a lixedand a rotating hearth. Y Fig. i represents on a scale intermediate between that of Fig. 1 and of Figs. 2and 3, a transverse section of one of the hearths.

The furnace shown in Fig. 1' comprises three fixed hearths 1, 2, 3 and two movable hearthsl, 5. Each fixed hearth is secured toa circular frame .6 provided at the exterior with a circular rail 7 mounted upon stationary supports, not shown. Each movable hearth as t is secured-to a circular frameS provided at the exterior with a circular rail 9 adapted to rest upon vertical rollers, not shown, whose axles are secured to a stationary structure. The said movable hearths are rotated by suitable means.

Each :fixed hearth consists of two halves 10, 11 made of refractory material, Fig. 2, mounted in the frame 12 and separated at the middleby a metallic rake 13 which consists of a diametrical tube connected at one end with the cooling water inlet conduit 14 and at the other end with the outlet conduit 15. The hollow rake 13 is preferably .provided at the interior with a vertical partition 16 making it more rigid and ensuring an increased water cooling surface, so that for a given circulation and within a given time the heat'removed will be greater than without the use of the said partition. Each arm of the rake 13 is provided on its lower surface with metallic teeth 17, 18, 19, etc., which are preferably cast in one with the rake and have the form, dimensions, disposition and inclination as set forth in said U. S. Patent No. 1,480,525.

"Each of the movable hearths as 1 consists of two halves 20, 21, Fig. 3 made of refractory material and mounted in the frame 22; between the said parts is disposed the rake 23 which is also mounted on said frame. The rake 23 is provided in each of its arms with a longitudinal partition 24, 25 extend- 'ing from the middle to within a short distance from the end of the rake. At the central part of the rake are formed, by walls of suitable shape, the two chambers 26, 27 one of which, 26, is connected for example with a central vertical tube 28 and with two chambers 2t, 25" situated on the same side of the partitions 24,25; the second chamber 27 is connected with a tube 29 coaxial with and surrounding the tube 28, as well as with the two chambers 24, 25" situated on the other side of the partitions 24, 25. The inner tube 28 is connected at the top with a supply tank 30, Fig. 1; the outer tube29 is closed at the top and is provided with a cock- 31 disposed above a water return tank 32. In this manner the cooling water from said supply tank proceeds through the innertube 28, the supply chamber 26, the two chambers 24, 25 of the rake arms, the two chambers 24, 25 of said arms, the chamber 27, the outer tube 29, and thence returns through the cock 31 to the tank 32. -Each rake of a movable hearth, ast, has at the lower part the teeth 33, 3'4, 35, etc., which are preferably cast in one with the rake, andin' the same manner as for the fixed hearths are given the forms, dimensions, disposition and inclination as mentioned in my above mentioned prior patent.

The outer tube 29 supplying the rake of the movable hearth 4 is provided with a downwardly extending flange 36 engaged in a trough 37 containing sand and disposed upon the rake of the upper fixed hearth 1, so as to form a tight joint in the manner al-' ready used in other pipes or furnaces. The lower movable hearth 5 is provided with solid teeth of refractory material as used in the known Spirlet furnaces, since these teeth, which act upon the last hearth which has now become considerably cooled by the air entering the furnace, are much less subject to damage.

The said furnace arrangement is operated in the following manner:

The ore in a suitably pulverized condition is introduced through an aperture in the upper fixed hearth 1 which is situated near the periphery and at the same distance from the centre as the farthest tooth of the set. The ore drops upon the upper movable hearth 4 which in the case represented by the figure, when turning in the counterclockwise direction, will bring the circular outer portion of the material adjacent the part of the tooth 17 which is farthest from the centre; said tooth will move this circular portion towards the centre, by a distance equal to the difference between the distances from the centre to its inner and its outer edge, while at the same time completely overturning the portion of material which is adjacent the tooth. The said portion of material which is thus moved towards the centre will then be brought adjacent the farthest tooth from the centre 17 upon the opposite arm of the rake. The material thus moved inwardly will then be brought adjacent the tooth 18 which overturns it and moves it still further towards the centre, and so on. The pulverized ore thus reaches the central region of the hearth 4; this portion is provided with apertures, not shown, through which it drops upon the fixed hearth 2, in the region covered by the tooth 33. The teeth 33, 34, 35, 33', 34, 35 are mounted in the contrary direction to the teeth of the rake of the upper fixed hearth 1. whereby the ore is caused to travel from the centre to the periphery of the fixed hearth 2, on the same principle as in the preceding case. The latter hearth is in turn provided with an aperture near the periphery in the region corresponding to the outer tooth. The ore is again brought towards the centre of the movable hearth 5 and is then dropped upon the lower fixed hearth 3 and is brought to the periphery by the rake teeth, not shown, of the movable hearth 5. At this point it is discharged in the known manner through the apertures 10 of a fixed frame 11 and falls into the receptacles 42 in which the material is contained. The air inlets 4L3 situated at the lower part of the brickwork provide for the admission of air through the lower part of the furnace, the air circulating in the furnace in the contrary direction to that of the travel of the ore.

As observed in the preceding description which sets forth the operation of the furnace, the arrangement according to the invention utilizes the entire surface of the hearths.

hat I claim is:

1. In a furnace for roasting ores having hearths of a refractory nature and circular form, which aresuperposed and are alternately fixed and rotating, an arrangement of furnace rakes cooled by water circulation comprising refractory hearths each consisting of two semicircular portions, a circular metallic frame supporting each hearth, a hollow diametrical metallic arm interposed between said portions of each hearth, means whereby a cooling fluid is enabled to circulate within said hollow arm and metallic rake teeth provided on said arm, which is supported by the circular frame of the. hearth.

2. In a furnace for roasting ores having hearths of a refractory nature and circular form, which are superposed and are alternately fixed and rotating, an arrangement of furnace rakes cooled by water circulation, as claimed in claim 1, in which the rakes for stationary hearths are hollow throughout the whole length, the water of circulation entering at one end and issuing from the other.

In witness whereof I have hereunto set my hand.

LUCIEN GESGI-IWIND. 

